I am by no means an expert on old tubes, but I recently picked up a quad of used Mullards that were said to have plenty of life left in them. The flashing is not bright/shiny on any of them, it's rather a dull grey color. But one of the four tubes is pictured below. To me, it looks like this tube is toast, and I would be loathe to run it in my amp for any period of time for fear of it giving up the ghost. There is no flashing left, and it just appears to be burned in the area where the flashing used to be. Is this tube good, or should I be asking for my money back?